The water supply from the Atlantic Ocean and the discharge
from a number of major rivers create a perfect climate for micro-organisms.
These ideal circumstances stimulate the development of plankton, which
forms the basis for an extensive food web. It is eaten by smaller animals
(worms, shellfish, small fish), which in turn fall prey to larger fish,
birds and marine mammals.

The
North Sea is a rich area and a very important fishing ground: 5% of the
world's total fish catch is caught here. However, fishing activity varies
sharply in the countries around the North Sea. The Belgian fish catch
accounts for just 1% of the total volume of fish caught in the North Sea,
which, in 1995 amounted to slightly less than 3.5 million tonnes in fish
and shellfish. Denmark and Norway in particular come out on top here,
with 45% and 22 % respectively. Herring, plaice, haddock and cod are the
main types of fish caught for human consumption.

Fishing has a major impact on all levels of the ecosystem.
Biotopes disappear because the seabed is disturbed, species are fished
to extinction, undersized fish are thrown back and eaten by scavengers
and birds, and mammals get caught in fishing nets.

At European level measures are being developed to protect
fish against overfishing and allow threatened species to recover. International
quotas are set (quantities that may be fished) and the European fleet
is being thinned out.